1. Field of Invention
The present invention relates to a friction device assembly structure for an automatic transmission in which an inner diameter of an end play adjustment element for adjusting the end play between a first friction device and a piston is designed such that a second friction device is prevented from interfering with the end play adjustment element, thus enhancing the ease of assembly of the friction device.
2. Description of Related Art
Generally, automatic transmissions include a torque converter, a gear shift mechanism which is connected to the torque converter to change the speed of the output of an engine, and a control circuit which selectively operates gears of the gear shift mechanism depending on the driving conditions of a vehicle.
In the gear shift mechanism of such an automatic transmission, a planetary gear device includes a sun gear, a ring gear and a carrier and controls rotation of the gears so that rotational force is transmitted from the torque converter to an output shaft at an appropriate gear shift ratio based on the relative motion of the gears.
Clutches, brakes, etc. are used to control the connection or interruption of the gears. A gear shift ratio is determined depending on the arrangement of the clutches and brakes or a change in their number, thereby realizing a desired gear speed.
FIG. 1 is a view illustrating the construction of a conventional brake used in an automatic transmission. A plurality of brake plates 3 are installed in a transmission casing 6 so as to be movable in a transverse direction. A plurality of brake discs 2 are provided on a circumferential outer surface of a rotary body 1 so as to be movable in the transverse direction. The rotary body 1 is coaxially provided with an input shaft of the transmission. The brake discs 2 and the brake plates 3 are provided in alternation.
A brake piston 5 is provided in a side of the brake. The operation of the brake piston 5 using hydraulic pressure puts the brake plates 3 and the brake discs 2 into close contact with each other under pressure, thus restraining the rotation of the rotary body 1 so that rotary elements of the planetary gear device connected to the rotary body 1 are fixed.
An end play adjustment plate 4 of a predetermined thickness is provided between the brake piston 5 and the corresponding brake plate 3 to adjust an end play Y therebetween. The end play adjustment plate 4 is installed in the transmission casing 6 so as to be movable in the transverse direction in the same manner as are the brake plates 3.
The end play adjustment plate does not cause any problems in the general gear shift mechanism. However, in a multi-step transmission structure, a comparatively small inner diameter of the end play adjustment plate interferes with other elements, which leads to several problems.
The inner diameter of the end play adjustment plate is equal to that of each brake plate and is smaller than the outermost diameter of a clutch assembly 7 that is disposed inside the brake assembly. During the assembly of the brake and clutch that form a friction device of the transmission, the end play adjustment plate interferes with peripheral elements such as the clutch assembly. This makes the work of re-assembling the end play adjustment plate difficult. To carry out the re-assembly of the end play adjustment plate, in addition to a main line along which the brake assembly and the clutch assembly are assembled, a buffer line must be added for the assembly of an oil pump.
In detail, after the brake assembly that includes the brake plates and the brake discs has been installed in the transmission casing, the end play adjustment plate is assembled with the brake assembly. The clutch assembly is thereafter assembled. The oil pump along with the brake piston is assembled.
If the end play between the brake piston and the end play adjustment plate is not suitable, the end play adjustment plate must be replaced. Here the cumbersome operation of having to separate the clutch assembly from the transmission and re-assemble it must be carried out. As such, to switch out the end play adjustment plate, the operations of separating the clutch assembly from the transmission and then re-assembling it are required. Therefore, the separate buffer line along which re-assembly of the end play adjustment plate and the clutch assembly and assembly of the oil pump are performed must be provided parallel to the main line. Such an additional assembly line increases the cost of equipment.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.